BABOMETJJICAL AND MHTHOKOUMIICAL OI5SKK V AT1()N> 



minimum between 1 and 7 p. m., and die equally-marked maximum bet 



the average amount of humidity has been very Bmall, and the different 



maxinmnr and minimum of tin" dav has been from two to three times 



PmTadelphia. All the features arc more distinctly marked than in loss exti 



In Woodruff Valley, at the end of .May. the sun rises about 





onrise minimum at Philadelpliia, or. rather, it depended upon the same agencies 



1, cause the extension of that inininnun beyond the Lour of sunrise. It was pro- 

 ed somewhat by the upward movement of the wanned air and the vapor contained 

 which began 'soon after sunrise, and by the circumstance that the little humidity 

 h h ;l< l neeumulated during the ni-ht in the soil was rapidly decreasing. Still the 

 •oration soon became so vigorous that it gained upon the other agencies, and at 8 

 . the maximum was reaehed, whieh, however, was not much above the point which 

 quantity Of vapor had attained at sunrise, just before the depression had taken 



L^nTof O^^insf^hUe tie air would have required at that time over 7 -rains 

 for its saturation with vapor. This was shortly Wore sunset, at the time when under 



sank nXe^d^ore' while a limn. ed evaporation continued, and both eauses eomhined 

 effected a gradual increase of the quantity of vapor, which continued until sunrise 

 The avera-e amount in one cubic foot was only 1.08 -rains, and the difference between 

 the largest and smallest amount 1.26 -rains troy. 



At Camp Floyd, in September, the maximum took place at 9 a.m., the minimum, 



grains of vapor in a cubic foot of air. The increase lasted then to midnight, when no 

 further change took place until after sunrise at ii a. m., when the increase commenced 

 again and lasted until the maximum was reached. The stability during the night, 



^71-!^^ havealready 



mentioned in that connection, namely, rising currents of air on a dry wind from the 



n,ore so when it happen, to he warm and dry. If it is warm and charged with moist- 

 ure it either increases the evaporation little or not at all, and if the station ,s much 

 colder, the moisture of the wind may even be precipitated. A cold wind does not 

 increase the evaporation so much, especially if it is itself charged with moisture, and 

 it can only create precipitation by cooling the air at the station below the point of sat- 



